HVAC systems have improved considerably in efficiency and utility from the early on-off systems where an entire volume was being conditioned as a function of a single thermostat. Building designs using skin facade structures and windows rather than more substantial exteriors tend to exaggerate thermal transmissions across the building exterior. Electrical office equipment and lighting can exhaust substantial heat, generally in the central area of a work space. Thus, heating and cooling requirements for an HVAC system tend to be a function of location within the volume served by the system.
With the advent of flexible control systems and the impetus of improved efficiency, zoned HVAC systems began to develop. Controlled zones can be arranged to provide for exterior spaces having a variety of solar heating loads and building thermal transmission loads and for interior spaces having a relatively constant and uniform cooling requirement from heat generated by the people, lighting and equipment in the interior space.
A typical early HVAC zoned system simply had two systems responding independently to the demands of the interior and exterior zones. One improvement was to space several exterior zones about the periphery to accommodate substantial changes in solar heat loads as a function of building exposure, seasonal changes and hourly variations in sun location. Typically, an interior zone has only cooling requirements and the air flow is controlled by dampers in air distribution ducts connected with a central air shaft. The exterior zone typically has a number of controllable sectors, with each sector having a thermostatic sensor, cooling air flow damper controls and an air heating system. The heating or cooling of each sector is controlled by the thermostatic sensor in that sector.
Applicant is also aware of a three zone HVAC distribution system. An interior zone is provided as described above. A first exterior zone is then provided around the interior zone to generally accommodate solar heating loads and a second exterior zone is provided about the first exterior zone to generally accommodate thermal transmissions through the building exterior facade. Each zone may include a plurality of sectors where each zone sector has a dedicated associated thermostatic control system. Further, each sector of each second exterior zone includes a heating system.
The three zone system generally described above offers some operational and efficiency improvements. However, a substantial amount of heating equipment is required to complete each second exterior zone sector. Further, adjacent sectors in a second exterior zone can become unstable where one sector is heating and the adjacent sector is cooling responsive to the heat input, and vice versa. A second exterior zone sector may even be trying to heat cooled air from the central air shaft.
These and other disadvantages of the prior art are overcome by the present invention, and an improved HVAC air transmission distribution and control system is provided.